Target Level Of Safety Research Articles

Reliability-based Assessment of the Structural Integrity of some Existing Reinforced Concrete Columns

Abnormal loading can initiate the progressive collapse of a reinforced concrete building. A progressive collapse may start as a local failure, followed by a sequence of reactions leading to a massive portion failure of an entire structure. Reinforced concrete columns are significant structural elements in ascertaining the integrity of framed buildings. This paper presents the report on the structural integrity of reinforced concrete columns of two selected university buildings labelled A and B investigated by using non-destructive testing techniques. First-Order Reliability Method (FORM) was deployed to process the data from the field in order to generate the implied safety indices for all accessed columns in the two buildings. The computed safety indices decrease as the simulated designed practical axial loads/moments increase for all the assumed steel ratios (0.4%, 1.59% and 6%) based on BS 8110:1997:1. When compared with the target safety level of 3.8 according to BS EN 1990:2002+A1:2005 for 50 years reference period of Class RC2 structural members in the ultimate limit state, almost all the columns passed the reliability test except the columns labelled 71 in building A; and C81A and C85 for building B. The highlighted critical columns show the direction for immediate repairs to forestall the initiation of eventual progressive failure of the buildings.

Research on the Collision Risk of Fusion Operation of Manned Aircraft and Unmanned Aircraft at Zigong Airport.

Low-altitude airspace is developing rapidly, but the utilization rate of airspace resources is low. Therefore, in order to solve the problem of the safe operation of the fusion of large UAVs and manned aircraft in the same airspace, this paper analyzes the theoretical calculation of the collision risk of the fusion operation of manned aircraft and UAVs at Feng Ming Airport in Zigong, verifying that while assessing the safety spacing of 10 km in the lateral direction, it further simulates the possibility of calculating the theoretical smaller safety spacing. The study will propose a new theory of error spacing safety margin and improve it according to the traditional Event collision risk model, combining the error spacing safety margin to establish an improved collision model more suitable for the fusion operation of manned and unmanned aircraft and reduce the redundancy of calculation. The error factors affecting manned and unmanned aircraft at Zigong Airport are analyzed, and theoretical calculations are analyzed by combining the actual data of Zigong Airport. Finally, the Monte Carlo simulation method is used to solve the error, substitute the calculation results, and simulate a section of the trajectory of the fusion operation for the reverse argument. The theoretical calculation results show that the collision risk from 10 km to 8 km satisfies the lateral target safety level (TSL) specified by ICAO under both traditional and improved models. The collision risk calculated by the improved model incorporating the error spacing safety margin is smaller, which enhances the safety of the model calculations. The results of the study can provide theoretical references for the fusion operation of manned and unmanned aircraft.

IM-based seismic reliability assessment of the pre-code masonry building stock in metropolitan area of Lisbon

Earthquakes have a long history of causing catastrophic damage to communities, resulting in structural collapses, loss of life, and economic turmoil. To enable informed decision-making and reduce the impact of these events in earthquake-prone regions, seismic risk studies provide relevant information to support stakeholders in the implementation of effective risk-based policies. The present work addresses the seismic reliability of the pre-code masonry building stock in the Metropolitan Area of Lisbon, which is the region of Portugal that faces the highest seismic risk due to the coexistence of moderate to high seismic hazard and highest demographic-economic exposure. The adopted general framework combines several hazard studies developed for the region under investigation and a synthetic database of masonry buildings representative of the pre-code building stock in Lisbon. Through analytical–numerical probabilistic approaches, new second-order hazard solutions with structural dependency are derived for the mean annual frequency of limit-state exceedance, which can be integrated into national application documents for Eurocode 8. In light of these results, the reliability assessment of the building stock is conducted in several Local Administrative Units by means of an improved SAC/FEMA formulation. The study represents the first comprehensive investigation of its kind in this region, providing essential information to define appropriate target safety level for code calibration and support future risk studies.

RUNWAY END SAFETY AREA: OVERRUN AND UNDERSHOT SAFETY RISK ANALYSIS

An airport is a complex facility for passenger and cargo processing, aircraft arrival, departure, and maintenance. Ensuring safe and comfortable flights for its passengers requires implementing aviation security and safety improvements in tandem with the growing number of aircraft in operation. Aviation operators and regulators are always focused on issues and potential incidents that jeopardize aviation safety and security, particularly during the landing and takeoff phases of flight, which include overrun and undershoot occurrences. Therefore, a study is required to determine the event’s probability. By adopting research methods that have been developed by the European Aviation Safety Agency (EASA), this research aimed to analyze the risk of overrun and undershoot at Sultan Syarif Kasim II Airport (SSK II) and Raja Haji Fisabilillah Airport (RHF). The research method is quantitative by comparing data collected with the Target Level of Safety (TLS), which is quantified and recommended by the aviation authority International Civil Aviation Organization (ICAO) and the British Civil Aviation Authority (CAA UK), where the acceptable TLS according to ICAO is 6.6 x 10-7 while according to the UK CAA it is 4 x 10-7. The result showed that the probability value of overrun and undershoot at SSK II Airport averages 0.66 x 10-7 and 2.98 x 10-7 at RHF Airport. This indicates that at RHF Airport, there is a higher possibility of overrun and undershooting risk frequency than at SSK II Airport. The fact that RHF Airport has just one RESA is the primary element affecting the high-risk likelihood at RHF Airport. The chance of overrun and undershoot occurrence frequency dropped to an average of 2.06 x 10-7 after simulating RESA compliance per ICAO regulations.

What are the appropriate target safety level and corresponding partial load safety factor for bolted joints on wind turbine tower frame?

During preassembly on the quayside, towers are temporarily erected on the tower frame through the supporting structures. The bottom of these structures is bolted on top of the tower frame. The degree of conservatism of applying the generic load safety factor (1.5) for the bolted joints on the tower frame has never been investigated. The objective of this study is to determine the cost-optimal target safety level and calibrate the partial load safety factor for these bolted joints. The target annual reliability index is obtained based upon a simplified cost model. The overturning bending moment is explicitly introduced to the limit state functions through the bending moment coefficient obtained in the wind tunnel tests. The load model uncertainty is quantified by a Bayesian analysis, based upon a full-scale single tower test data. The case study will justify the applicability of the approach and the possibility of decreasing the environmental partial load safety factor for bolted joints. The cost-optimal target safety level and the corresponding load safety factor can significantly help to avoid the unnecessary conservatism in designing the bolted joints on tower frame, which helps the management make decision on economic development strategy of tower frames in the future.

Research on Lateral Safety Spacing for Fusion Operation Based on Unmanned and Manned Aircraft-Event Modeling.

With the rapid development of unmanned aerial vehicle technology and its increasing application across various fields, current airspace resources are insufficient for unmanned aerial vehicles' needs. This paper, taking Zigong General Aviation Airport in Sichuan as a case study, explores the lateral safety spacing in a mixed operation mode of unmanned aerial vehicles and manned aircraft. Currently, there are no standardized regulations for the safe spacing of the fusion operation of unmanned and manned aircraft. Theoretical research is essential to provide a reference for actual operations. It introduces the UM-Event (unmanned and manned aircraft-event) collision risk model, an adaptation of the Event collision risk model, considering factors like communication, navigation, surveillance performance, human factors, collision avoidance equipment performance, and meteorology. Safety spacing was determined via simulation experiments and actual data analysis, adhering to the target safety level (TSL). Findings indicate that surveillance performance has a minor impact on safety spacing, while communication and navigation significantly influence it. The safety spacing, influenced solely by CNS (communication performance, navigation performance, surveillance performance) and combined factors, increased from 4.42 to 4.47 nautical miles. These results offer theoretical guidance for unmanned aerial vehicle safety in non-segregated airspace.

Evaluation of Airspace Operation Safety Level based on PMS

The point merge (PM) flight procedure is a new type of flight procedure of performance -based navigation (PBN). The capacity of the point merge procedure is evaluated through the parameters of the point merge flight procedure. Through the parameters of the point merge flight procedure and the parameters of the aircraft flying in the point merge flight procedure, the collision risk between two aircraft in the merge area and the overall collision risk of the aircraft in the point merge procedure are calculated. The evaluation methods and calculation formulas of these three parameters are summarized, and a reasonable method of airspace operation safety level evaluation based on point merge system (PMS) is sought. The inferred method of airspace operation safety level evaluation based on PMS is to compare the operation capacity with the calculated theoretical capacity, and compare the collision risk between two aircraft in the fusion area calculated according to track data and radar data and the overall collision risk of aircraft in PMS with the target safety level specified by China’s air transportation industry.

ASD and LRFD: Reliability comparison for designs subjected to wind loads

Current design practice in the United States allows engineers to use either Allowable Strength Design (ASD) or Load and Resistance Factor Design (LRFD) method, under the assumption that both methods provide similar levels of economy (available design strengths) and safety (probabilities of failure and reliability indices) regardless of the design conditions. Recent studies have demonstrated that significant differences in economy can arise between ASD- and LRFD-based designs subjected to combinations of gravity and wind loads, suggesting inconsistencies between the safety levels. This study investigates the safety levels provided by the ASD and LRFD methods for such design cases. The safety levels were estimated using a formal reliability analysis with consideration of geometrically non-linear second-order effects. The reliability analysis was performed using Monte Carlo simulations with appropriate probability distributions for the random variables associated with both resistance and loads. The findings of this study indicate that generally accepted uniformity of reliabilities achieved by the ASD and LRFD methods does not hold for design cases governed by wind loads. The safety levels achieved by using the ASD method are less consistent than those achieved by using the LRFD method. The use of the ASD method generally entails the acceptance of failure risks many times greater than for those of the LRFD method, and target safety levels lower than those stipulated by the ASCE 7 Standard. These results highlight the need for a reevaluation of the current design practices to ensure that the required target levels of structural safety are consistently met.

Quantifying Specific Operation Airborne Collision Risk through Monte Carlo Simulation

Integration of Uncrewed Aircraft into unsegregated airspace requires robust and objective risk assessment in order to prevent exposure of existing airspace users to additional risk. A probabilistic Mid-Air Collision risk model is developed based on surveillance traffic data for the intended operational area. Simulated probable traffic scenarios are superimposed on a desired Uncrewed Aircraft operation and then sampled using Monte Carlo methods. The results are used to estimate the operation-specific collision probability with known uncertainty in the output. The methodology is demonstrated for an example medical logistics operation in the United Kingdom, and a Target Level of Safety is used as a benchmark to decide whether the operation should be permitted.

Parametric Study of Structured UTM Separation Recommendations with Physics-Based Monte Carlo Distribution for Collision Risk Model

With the increasing demand for unmanned aircraft system (UAS) traffic management (UTM) airspace comes the need to ensure the safe operation and management of said airspace. One layer of defense against mid-air-collision and the ensuing third-party injury or fatality is the pre-flight separation assurance. This could be achieved by establishing the separation requirements for the UTM traffic based on the flight dynamics and communication navigation surveillance (CNS) performance that could be achieved in the airspace in question. A modified Reich collision risk model, typically used in civil aviation for separation minima evaluation, was used for the evaluation of the initial separation that would meet the target level of safety within a prescribed look-ahead time. This paper presents the parametric evaluation of using this physics-based and Monte Carlo-driven Reich collision risk model to evaluate the separation recommendation needed to achieve 10−7 mid-air-collision risk in UTM. The evaluation was conducted for an encounter pair consisting of identical ∼1.2 kg quadrotors with various encounter geometries, cruise velocities, navigation uncertainties, and communication latency.

Ground Risk Estimation of Unmanned Aerial Vehicles Based on Probability Approximation for Impact Positions with Multi-Uncertainties

In this paper, a methodology to assess ground risk with multi-uncertainties is introduced, which is associated with a major unmanned aerial vehicle (UAV) in-flight incident. In the assessment model, random factors are taken into account including uncertainty in the drag force, uncertainty in the UAV velocity, and the random effects of local wind. The probability distribution of impact positions is first estimated by using a second-order drag model with probabilistic assumptions regarding the least well-known parameters. Then, an approach for modeling and estimating the ground risks is presented, in which the ground casualties are set as the safety index. In the multifactor risk estimation model, ground casualty areas covered by the UAVs’ debris are determined. Correspondingly, the probability of fatal injuries to people is derived by addressing the protection effects, impact energy, and energy threshold a person can sustain. Further, four kinds of sheltering effects are defined. Finally, the affected area on the ground is partitioned into six zones, taking into consideration the density and distribution of the local population. Case studies are conducted for fixed-wing and rotary-wing UAVs. Risk levels on the ground are obtained and compared with the widely accepted target safety level of manned aircrafts.

Non-Intersecting Diverging Runways Separation under Emergency Avoidance Situation

Although runway separation, based on the probability of collision, has been studied for decades, the mathematical methods proposed by the majority of studies cannot handle complex situations, such as the operation of non-intersecting diverging runways at an airport with multiple runways. By applying a combination method of computer simulation and collision probability calculation, the arrival and departure window (ADW) separation for non-intersecting diverging runways of a multi-runway airport was studied under the emergency avoidance (EA) situation. Combining the example of runways 01L/19R and 11L of Beijing Daxing Airport, the ADW separation settings for the airport’s northward and southward operations were determined to meet the target level of safety. Moreover, the effects of range-type parameters on the ADW separation were quantified. When the EA maximum speed limit and EA minimum climb rate were 200 kt (102.9 m/s) and 10%, respectively, the results were such that no ADW separation was required for northward operation, and the ADW separation was from 3.2 km to 7.1 km for southward operation. Furthermore, the results showed that the proposed method could more accurately describe the nominal trajectories of aircraft and improve the precision of collision probability calculation. Meanwhile, the sensitivity analysis method for range-type parameters could help airports and air traffic control facilities to set reasonable constraints to improve theoretical runway capacity, while satisfying practical feasibility.

Risk-Based Method for Determining Separation Minima in Unmanned Aircraft Systems

Risk assessment is a key issue in enabling the use of unmanned aircraft systems (UASs) in nonsegregated areas, especially in very low-level airspace and urban areas. The specific operations risk assessment (SORA) methodology represents an important milestone in performing the risk assessments required by aviation safety agencies to UAS operators in specific operations. However, the SORA is a qualitative method used for UASs operating inside a well-bounded operational volume. This paper proposes a quantitative method that can not only be used in a closed volume but also in an airspace shared by several UAS missions and even general aviation. The basis for this is providing a separation volume (a “bubble”) to prevent collisions that is calculated using a risk-based approach. The method consists of setting a target level of safety, which is accomplished using a tradeoff between strategic and tactical mitigations. A probabilistic methodology for performing quantitative risk assessment of strategic and tactical mitigations is provided, and the dependence of the separation distance is carefully analyzed. All factors affecting the separation distance are identified, and their contributions to collision risk are probabilistically estimated. The method takes into account specific factors relating to UASs such as trajectories, separation methods, and performance. As a result, the method allows numerical determination of a separation distance for a given target level of safety and an operational scenario.

Deep generative modelling of aircraft trajectories in terminal maneuvering areas

Airspace design is subject to a multitude of constraints, which are mainly driven by the concern to keep the risk of mid-air collision below a target level of safety. For that purpose, Monte Carlo simulation methods can be applied to estimate aircraft conflict probability but require the accurate generation of artificial trajectories. Generative models allow to generate an infinite number of trajectories for air traffic procedures where only few observations are available. The generated trajectories must not only resemble observed trajectories in terms of statistical distributions but they should stay flyable and consider uncertainty due to weather, air traffic control, aircraft performances, or human factors. This paper focuses on the generation problem, and its main contribution lies in the adaptation of the Variational Autoencoder structure to the problem of 4-dimensional aircraft trajectories modelling using Temporal Convolutional Networks and a prior distribution composed of a Variational Mixture of Posteriors (VampPrior). The proposed model has been trained on trajectories in the Terminal Manoeuvre Area of Zurich airport, which have a particularly high degree of variability as air traffic controllers often take actions that deviate aircraft from the nominal approach procedure. The model has demonstrated great abilities to take into account such amount of uncertainty. Regarding metrics that evaluate the estimation of the statistical distribution of the observed trajectories, and the flyability of the generated ones, the proposed method outperforms traditional statistical methods by being able to generate more complex and realistic trajectories.

Collision risk assessment of reduced aircraft separation minima in procedural airspace using advanced communication and navigation

With the advancement of Communication, Navigation and Surveillance (CNS) technologies such as space-based Automatic Dependent Surveillance-Broadcast/Contract (ADS-B/C), large separation minima may be reduced in procedural airspaces. It is of great significance to know the upper limit of the Reduced Separation Minima (RSM) for a procedural airspace and the corresponding consequences on collision risk with specifics of the advanced ADS-B and control intervention model. In this work, an interactive software is first developed for collision risk estimation. This software integrates the International Civil Aviation Organization (ICAO) collision risk models for lateral and longitudinal collision risk calculation for the Singapore procedural airspace. Results demonstrate that the lateral and longitudinal collision risk of Singapore procedural airspace with respect to current control procedures meets the ICAO Target Level of Safety (TLS) standard. Moreover, the feasibility of reducing the horizontal separations implemented in the Singapore procedural airspace with respect to advanced CNS techniques is investigated. It is found that if advanced CNS technologies are applied, then the current 50-NM lateral and longitudinal separation standards can be reduced to 22 NM (1 NM = 1.825 km) and 20 NM, respectively, to meet the TLS standards based on current demand. A method is then devised to expand the traffic demand by p for p ∈ [10%, 200%]. It is found that the minimum lateral and longitudinal separations can be reduced from 50 NM to be within the range of [23, 31] NM, and 20 NM, respectively, for p ∈ [10%, 200%], while the collision risk still meets the TLS standards.

도심 항공 모빌리티와 장애물 간의 감시장비 기반 충돌 위험도 평가모형

Urban Air Mobility is expected to resolve some problems in urban transportation such as traffic congestion and air pollution. Various studies for a large-scale commercialization of UAM are being actively conducted. To that end, the UAM Traffic Management system aims at securing a safety and an efficiency of UAM operations. In this study, a risk assessment model is proposed to evaluate the risk of collision between a vehicle and surrounding obstacles. The proposed model is conceived from the past studies for determining a proper separation distance between parallel runways for their independent operations. The model calculates the risk that the surveillance system fails to meet a target level of safety for a given buffer zone size between a designed route and surrounding obstacles. The model is applied to one of the routes proposed in K-UAM roadmap to evaluate its performances.

Fragility analysis of existing prestressed concrete bridges under traffic loads according to new Italian guidelines

AbstractAfter the 2018 collapse of Morandi highway bridge in Genova, new Italian guidelines (GL) were issued for prioritization of safety evaluations and retrofit interventions on existing bridges. Among several novelties, GL introduced new traffic load models (TLMs) which can be adopted for existing bridges in case of noncompliant safety checks according to the Italian building code (NTC) provisions. In this study, a class of simply supported, beam‐type, prestressed concrete bridge decks built between 1970 and 1980 in Italy is considered. Assuming geometric, material, and load random variables together with consideration of capacity model uncertainty, Monte Carlo sampling technique was implemented in MATLAB in order to randomly generate deck models and to evaluate their traffic‐load fragility. Fragility analysis was carried out to compare vulnerability levels of existing Italian bridges under different load patterns provided by GL and NTC. In addition to a prescribed TLM, the sensitivity of fragility to bridge usage limitations, such as reduced distance of external load lane from kerb or reduced number of lanes, was also quantified to support decision‐making by road management companies. In the final part of the study, the annual failure probability of selected bridges was estimated using a European weigh‐in‐motion database and convolution of fragility and hazard. Analysis results show that structural fragility significantly depends on the load pattern, indicating that more realistic vehicle models should be developed to achieve a target safety level conforming to modern codes for constructions.

Risk-Based UAV Corridor Capacity Analysis above a Populated Area

To integrate unmanned aerial vehicles (UAVs) into the national airspace in a safe manner, a risk-based approach to the regulation of UAVs is adopted in many countries. Thus, the capacity to permit UAVs in urban airspace also needs to be evaluated in a risk-based sense. In this regard, this paper proposes a methodology to analyze the capacity of UAV corridors on the basis of third-party risk on the ground. By linking the collision rate of the corridor and the failure rates of UAVs with the number of fatalities on the ground, the capacity of the UAV corridor is derived to satisfy the target level of safety. To model the collision rate of UAVs in the corridor, the Reich collision risk model is utilized. Moreover, a ground risk map is generated to compute the third-party risk on the ground using the databases for Seoul, Korea. The results show that the failure rate of UAVs is the dominant factor for determining the capacity of the corridor, even if the number of corridors increases. The proposed methodology could be useful to manage the number of flights for applications where the UAV corridor is fixed and flight continues, such as package delivery.

Resistance factors for reliability based-design of fiber reinforced concrete suspended slabs in flexure

Due to the inherent uncertainties in the properties of construction materials, fabrication processes, applied loads, and the approximate nature of analysis methods, modern design codes have adopted the Load and Resistance Factor Design format (LRFD) to design civil engineering structures. In this format, loads and resistance are factored to consider the random nature of design variables. For instance, the reinforced concrete suspended slabs design is covered by ACI 318 [(Committee 318, 2019) 11 code, which is currently based on the LRFD format. On the other hand, the design of fiber reinforced concrete suspended (FRC) slabs fall under ACI 544.4 [(Committee 544, 2018) 22, which is not based on LRFD; therefore, it warrants an appropriate resistance factor to be used in conjunction with the current ASCE 7 [(American Society of Civil Engineers, 2017) 33 load factors and load combinations. In this paper, a reliability-based design procedure is developed to calibrate the resistance factor for the flexural design of FRC slabs with and without conventional steel reinforcement. Statistical and probabilistic analyses of experimental data showed that the resistance model for the flexural design of hybrid FRC slabs obeys the lognormal distribution with a bias of 1.33 and a coefficient of variation of 0.24. But for FRC slabs without additional reinforcement, the bias factor and the coefficient of variation of the resistance model increase to 1.56 and 0.37, respectively. In the case of conventional reinforced concrete slabs, the current resistance factor is . In the case of FRC slabs, an additional resistance factor of shall be applied to account for the contribution of fibers. This factor consistently provides the minimum safety level (i.e., the reliability index is close to or larger than the target reliability). However, in the case of FRC slabs without conventional steel reinforcement, a resistance factor of 0.75 is recommended to consistently meet the target safety level. The effectiveness of fibers in hybrid reinforced concrete slabs is more pronounced (smaller reduction of compared to 25% for slabs with fibers alone), thus, supporting the synergetic effect between the two reinforcing materials.

Load and resistance factor design versus reliability-based design of shallow foundations

ABSTRACT The load and resistance factor design (LRFD) approach employed in geotechnical design codes is often calibrated using the reliability-based design (RBD) method. However, the LRFD may not achieve the target safety level exactly. This paper makes comparisons between the LRFD and RBD by considering the ultimate and serviceability limit state design of strip foundations. The RBD is carried out via the Random Finite Element Method. It is found that the failure probability and the resulting foundation width for ULS obtained using the RBD increase with the soil spatial correlation length, gradually reaching a plateau. The comparison between the LRFD and RBD results for ULS suggests that the LRFD is conservative for low to medium soil variability, particularly at smaller correlation lengths. The reliability-based SLS design is less dependent on the soil correlation length, particularly for lower coefficients of variation of the soil elastic modulus. However, a resistance factor of 1.0 for SLS is unconservative, and resistance factors of 0.65, 0.7 and 0.8 are better aligned with the RBD when the target failure probabilities are 1×10−3, 1×10−2 and 1×10−1. The current study can be used to guide the design of shallow foundations and the calibration of the LRFD approach.